Small fish, large river: Surprisingly minimal genetic structure in a dispersal-limited, habitat specialist fish.

Genetic connectivity is expected to be lower in species with limited dispersal ability and a high degree of habitat specialization (intrinsic factors). Also, gene flow is predicted to be limited by habitat conditions such as physical barriers and geographic distance (extrinsic factors). We investigated the effects of distance, intervening pools, and rapids on gene flow in a species, the Tuxedo Darter (Etheostoma lemniscatum), a habitat specialist that is presumed to be dispersal-limited. We predicted that the interplay between these intrinsic and extrinsic factors would limit dispersal and lead to genetic structure even at the small spatial scale of the species range (a 38.6 km river reach). The simple linear distribution of E. lemniscatum allowed for an ideal test of how these factors acted on gene flow and allowed us to test expectations (e.g., isolation-by-distance) of linearly distributed species. Using 20 microsatellites from 163 individuals collected from 18 habitat patches, we observed low levels of genetic structure that were related to geographic distance and rapids, though these factors were not barriers to gene flow. Pools separating habitat patches did not contribute to any observed genetic structure. Overall, E. lemniscatum maintains gene flow across its range and is comprised of a single population. Due to the linear distribution of the species, a stepping-stone model of dispersal best explains the maintenance of gene flow across its small range. In general, our observation of higher-than-expected connectivity likely stems from an adaptation to disperse due to temporally unstable and patchy habitat.

Diversity within the Redeye Bass, Micropterus coosae (Perciformes: Centrarchidae) species group, with descriptions of four new species.

The Redeye Bass, Micropterus coosae, was described from the Mobile River basin, Chattahoochee, and Savannah rivers in Alabama and Georgia, USA, by Hubbs and Bailey (1940). At that time the authors recognized significant variation in the Black Warrior River population, and noted that with further study this form may be recognized as a separate taxon. An examination of variation in morphology and mitochondrial DNA supported this observation, and highlighted additional species-level variation, resulting in descriptions of a total of four new species: Micropterus cahabae, new sp., restricted to the Cahaba River system; Micropterus tallapoosae, new sp., restricted to the Tallapoosa River system; Micropterus warriorensis, new sp., from the Black Warrior River system; and Micropterus chattahoochae, new sp., from the Chattahoochee River system. Micropterus coosae is restricted to the Coosa River system. The new species differ from each other and from M. coosae by a combination of pigmentation and scale count characteristics, development of the tooth patch, and divergence within the ND2 gene. While two of these species are relatively common in upland streams within their ranges, M. warriorensis, M. cahabae and M. chattahoochae are uncommon and may warrant protection.

Timing of clade divergence and discordant estimates of genetic and morphological diversity in the Slender Madtom, Noturus exilis (Ictaluridae).

Phylogeographic relationships, the timing of clade diversification, and the potential for cryptic diversity in the Slender Madtom, Noturus exilis, was investigated using mitochondrial Cyt b, nuclear RAG2, shape analysis, and meristic and pigmentation data. Three well-supported and deeply divergent clades were recovered from analyses of genetic data: Little Red River (White River drainage) clade, Arkansas+Red River (Mississippi River) clade, and a large clade of populations from the rest of the range of the species. Recovered clades showed little to no diagnostic morphological differences, supporting previous hypotheses of morphological conservatism in catfishes, and indicating morphology may commonly underestimate diversity in this group of fishes. The Little Red River clade is the most distinct lineage of N. exilis with 11 POM pores (vs. 10 in other populations) and unique Cyt b haplotypes and RAG 2 alleles. However, treating it as a species separate from N. exilis would imply that the other major clades of N. exilis are more closely related to one another than they are to the Little Red River clade, which was not supported. The UCLN age estimate for Noturus was 23.9mya (95% HPD: 13.49, 35.43), indicating a late Oligocene to early Miocene origin. The age of N. exilis was estimated as late Miocene at 9.7mya (95% HPD: 5.32, 14.93). Diversification within the species spanned the late Miocene to mid-Pleistocene. The largest clade of N. exilis, which dates to the late Miocene, includes populations from the unglaciated Eastern and Interior Highlands as well as the previously glaciated Central Lowlands. Diversification of this clade coincides with a drastic drop in sea-level and diversification of other groups of Central Highlands fishes (Centrarchidae and Cyprinidae). Sub-clades dating to the Pleistocene show that northern populations occurring in previously glaciated regions resulted from dispersal from populations in the Ozarks up the Mississippi River following retreat of the Pleistocene glaciers. Pre-Pleistocene vicariance, such as drainage pattern changes of the Mississippi River, also played a prominent role in the history of the species. The incorporation of a temporal estimate of clade diversification revealed that in some instances, phylogeographic breaks shared with other aquatic species were best explained by different or persistent vicariant events through time, rather than a single shared event.

Sex differences in the correlation of emotional control and amygdala volumes in adolescents.

We examined male and female adolescents (8-18 years of age) that were scanned with structural brain MRI and looked for a correlation between volume of the right or the left amygdala and parent-reported ability of emotional control. A sex difference was found in the correlation between emotional control and the corrected volume of the left amygdala (that is the amygdala volume adjusted for total cranial volume). In girls, smaller left amygdala volumes were associated with better emotional control. In boys, larger left amygdala volumes were associated with better emotional control. These findings suggest that healthy girls and boys show a difference in the correlation between parental reports of emotional control and the left amygdala volume.

Discordant molecular and morphological evolution in buffalofishes (Actinopterygii: Catostomidae).

Buffalofishes (Genus Ictiobus) are large, robust-bodied suckers adapted to large rivers and lakes of North America. Currently recognized species are readily diagnosed by morphological characters, and the group is known from fossils dating back to the Miocene. However, sympatrically occurring species in the Mississippi River Basin are known to hybridize in nature and in the laboratory. Here we describe patterns of morphological (morphometric) and DNA sequence variation (mitochondrial and nuclear genes) across the geographic ranges of extant species of genus Ictiobus. We show that Ictiobus species form more of less discrete entities based on body morphometry, consistent with current taxonomy. However, except for I. labiosus, there is extensive sharing of alleles of nuclear and mitochondrial genes among species, and the species do not form reciprocally monophyletic groups in nuclear or mitochondrial gene trees. Moreover, the pattern is not confined to the broad area of sympatry in the Mississippi River Basin. We attribute this to a long history of introgressive hybridization and gene flow among species inhabiting the present-day Mississippi River Basin, and recent colonization of the Great Lakes, Hudson Bay drainage and gulf coastal rivers east and west of the Mississippi River by introgressed Mississippi River Basin stocks.

Abnormal development of the anterior cingulate in childhood-onset schizophrenia: a preliminary quantitative MRI study.

The anterior cingulate is a key component of neural networks subserving attention and emotion regulation, functions often impaired in patients with psychosis. The study aimed to examine anterior cingulate volumes and sulcal morphology in a group of patients with childhood-onset schizophrenia (COS) compared with controls. Brain magnetic resonance imaging (MRI) scans were obtained in 13 COS and 18 matched control children, ages 6-17 years. Volume measures for the anterior cingulate gyrus (ACG) were obtained through manual labeling. A determination of cingulate sulcal pattern (single or double) was made for each hemisphere. The COS group had a reduced leftward skew of the double cingulate sulcal pattern, and absence of the normal left>right ACG volume asymmetry. The right ACG was larger in the COS than in controls. The schizophrenic children showed decreases in all ACG volumes with age, while the controls showed increases or no change. The data suggest that significant cingulate abnormalities may result from deviations in progressive neurodevelopmental processes, beginning before birth and continuing through childhood and adolescence, in persons who develop schizophrenia. These structural differences may relate to the well-described cognitive deficits these children display, and to the cardinal symptoms of schizophrenia.

Superior temporal gyrus differences in childhood-onset schizophrenia.

The posterior superior temporal gyrus (STG) is the approximate site of Wernicke's area, a language region, which in previous studies has been reported to be abnormal in adults with schizophrenia. The present study assesses volumetric differences in the superior temporal gyrus of subjects with childhood-onset schizophrenia (COS). MRI scans of 18 subjects diagnosed with childhood-onset schizophrenia and 16 age- and sex-matched normals were analyzed to assess possible volume differences. The COS subjects displayed significant enlargement of the right posterior superior temporal gyrus, showing white matter increases bilaterally in this region. Our findings are consistent with studies that have found increased volumes in temporal lobe regions in COS and may provide a possible neural correlate for the language impairment observed in COS patients.

Gender differences in the left inferior frontal gyrus in normal children.

This study examined frontal lobe subregions in 46 normal children and adolescents (25 females, mean age: 11.08, SD: 3.07; and 21 males, mean age: 10.76, SD: 2.61) to assess the effects of age and gender on volumetric measures as well as hemispheric asymmetries. Superior, middle, inferior, and orbito-frontal gray, white, and cerebrospinal (CSF) volumes were manually delineated in high-resolution magnetic resonance imaging (MRI) data to assess possible morphological changes. We report a significant age-related increase in the white matter of the left inferior frontal gyrus (IFG) in boys (P = 0.007). Additionally, the left IFG was significantly larger in boys compared to girls (P = 0.004). Boys showed increased gray matter volume relative to girls even after correcting for total cerebral volume. Also, boys were found to have significant Right > Left asymmetry patterns with greater right hemispheric volumes for total cerebral volume, total cerebral white matter, MFG white matter, and SFG white matter (P < 0.001). Girls showed significant Right > Left asymmetry patterns in total cerebral and SFG white matter (P < 0.001). These findings suggest continued modification of the IFG during normal development in boys, and significant gender differences in IFG gray matter between boys and girls that may be possibly linked to gender differences in speech development and lateralization of language.

Thought disorder and nucleus accumbens in childhood: a structural MRI study.

Thought disorder has been described as a hallmark feature in both adult and childhood-onset schizophrenia. The nucleus accumbens (NAc) has been repeatedly proposed as a critical station for modulating gating of information flow and processing of information within the thalamocortical circuitry. The aim of the present study was to investigate the relationship of thought disorder measures, which were administered to 12 children with schizophrenia and 15 healthy age-matched controls, and NAc volumes obtained from high-resolution volumetric magnetic resonance imaging analyses. The propensity for specific thought disorder features was significantly related to NAc volumes, despite no statistically significant differences in the NAc volumes of children with schizophrenia and normal children. Smaller left NAc volumes were significantly related to poor on-line revision of linguistic errors in word choice, syntax and reference. On the other hand, underuse of on-line repair of errors in planning and organizing thinking was significantly associated with decreased right NAc volumes. The results of this pilot study suggest that the NAc is implicated in specific thought patterns of childhood. They also suggest that subcortical function in the NAc might reflect hemispheric specialization patterns with left lateralization for revision of linguistic errors and right lateralization for repair strategies involved in the organization of thinking.

Anterior cingulate, gyrus rectus, and orbitofrontal abnormalities in elderly depressed patients: an MRI-based parcellation of the prefrontal cortex.

OBJECTIVE: To examine structural abnormalities in subregions of the prefrontal cortex in elderly patients with depression, the authors explored differences in gray matter, white matter, and CSF volumes by applying a parcellation method based on magnetic resonance imaging (MRI). METHOD: Twenty-four elderly patients with major depression and 19 group-matched comparison subjects were studied with high-resolution MRI. Cortical surface extraction, tissue segmentation, and cortical parcellation methods were applied to obtain volume measures of gray matter, white matter, and CSF in seven prefrontal subregions: the anterior cingulate, gyrus rectus, orbitofrontal cortex, precentral gyrus, superior frontal cortex, middle frontal cortex, and inferior frontal cortex. RESULTS: Highly significant bilateral volume reductions in gray matter were observed in the anterior cingulate, the gyrus rectus, and the orbitofrontal cortex. Depressed patients also exhibited significant bilateral white matter volume reductions and significant CSF volume increases in the anterior cingulate and the gyrus rectus. Finally, the depressed group showed significant CSF volume reductions in the orbitofrontal cortex relative to the comparison subjects. None of the other regions examined revealed significant structural abnormalities. CONCLUSIONS: The prominent bilateral gray matter deficits in the anterior cingulate and the gyrus rectus as well as the orbitofrontal cortex may reflect disease-specific modifications of elderly depression. The differential pattern of abnormalities detected in the white matter and CSF compartments imply that distinct etiopathological mechanisms might underlie the structural cortical changes in these regions.

Proton magnetic resonance spectroscopic imaging of the brain in childhood autism.

BACKGROUND: Autism is a developmental disorder of unknown neurologic basis. Based on prior work, we used proton magnetic resonance spectroscopic imaging ((1)H- MRSI) to investigate brain structures, including cingulate and caudate, that we hypothesized would reveal metabolic abnormalities in subjects with autism. METHODS: In 22 children with autism, 5 to 16 years old, and 20 age-matched healthy control subjects, (1)H-MRSI assessed levels of N-acetyl compounds (NAA), choline compounds (Cho), and creatine plus phosphocreatine (Cr) at 272 msec echo-time and 1.5 T. RESULTS: In subjects with autism compared with control subjects, Cho was 27.2% lower in left inferior anterior cingulate and 19.1% higher in the head of the right caudate nucleus; Cr was 21.1% higher in the head of the right caudate nucleus, but lower in the body of the left caudate nucleus (17.9%) and right occipital cortex (16.6%). CONCLUSIONS: Results are consistent with altered membrane metabolism, altered energetic metabolism, or both in the left anterior cingulate gyrus, both caudate nuclei, and right occipital cortex in subjects with autism compared with control subjects.

Cortical sulcal maps in autism.

This study presents the first three-dimensional mapping of cortical sulcal patterns in autism, a pervasive developmental disorder, the underlying neurobiology of which remains unknown. High-resolution T(1)-weighted MRI scans were acquired in 21 autistic (age 10.7 +/- 3.1 years) and 20 normal control (age 11.3 +/- 2.9) children and adolescents. Using parametric mesh-based analytic techniques, we created three-dimensional models of the cerebral cortex and detailed maps of 22 major sulci in stereotaxic space. These average maps revealed anatomic shifting of major sulci primarily in frontal and temporal areas. Specifically, we found anterior and superior shifting of the superior frontal sulci bilaterally (P < or = 0.0003), anterior shifting of the right Sylvian fissure (P = 0.0002), the superior temporal sulcus (P = 0.0006 right, P = 0.02 left) and the left inferior frontal sulcus (P < or = 0.002) in the autistic group relative to the normal group. Less significant sulcal shifts occurred in the intraparietal and collateral sulci. These findings may indicate delayed maturation in autistic subjects in these brain regions involved in functions including working memory, emotion processing, language and eye gaze.